Insect Behaviour

Radiotelemetry unravels movements of a walking insect species in heterogeneous environments


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Fabrice Vinatier^a, Anaïs Chailleux^a, Pierre-François Duyck^{a, ,} , Frédéric Salmon^b, Françoise Lescourret^c and Philippe Tixier^a

^a CIRAD, Unité Systèmes de culture bananes, plantains et ananas, France

^b CIRAD, Unité Amélioration génétique d'espéces à multiplication végétative, France

^c INRA, Unité Plantes et Systèmes de culture Horticoles, France

 

The study of movements of individual organisms in heterogeneous environments is of primary importance for understanding the effect of habitat composition on population patterns. We developed a new experimental methodology to measure individual movements of walking insects, based on radiotracking. Our aims were to understand the link between habitat heterogeneity and moving patterns, and to characterize the movements with dynamic models of diffusion. We tracked individual movements of adults of Cosmopolites sordidus (Coleoptera: Curculionidae) with passive radio frequency identification (RFID) tags under different field management practices. Diffusion models based on recapture data indicated a subdiffusive movement of this species. Substantial variation was found between individual paths, but this variation was not sex dependent. Movement of released C. sordidus was affected by banana planting pattern and the presence/absence of crop residues but not by the presence of a cover crop between rows of bananas or by banana variety. These results show that the RFID technology is useful for evaluating the dispersal parameters of cryptic insects in heterogeneous environments.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 221-229

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Host plants and immatures as mate-searching cues in Heliconius butterflies

 

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Catalina Estrada ^{, a,} and Lawrence E. Gilbert^{1, a}

^a Integrative Biology, University of Texas at Austin, U.S.A.

 

The study of interactions between phytophagous insects and their host plants extends beyond understanding how insects deal with plant chemical defences. Sexual behaviour of these herbivores is integrated in several ways with host plants, as the latter influence timing and location of reproduction, and can provide clues for finding mates. Nevertheless, while numerous studies link butterfly evolution to host plant adaptations, the influence of plants on butterfly sexual behaviour has been little studied. We conducted experiments to determine the role of host plant cues in mate-searching behaviour of Heliconius charithonia butterflies. This species exhibits precopulatory mate guarding behaviour, wherein males find and perch on pupae, then copulate with eclosing females (‘pupal mating’). We found that males (1) visited plants damaged by feeding larvae more often than they visited undamaged plants and (2) displayed searching behaviour around the plant and in front of larvae, suggesting that odours signal the location of potential partners (pupae). Although males were attracted to common plant odours released after tissue damage, plants damaged by heterospecific butterfly larvae were less attractive, indicating that species recognition can occur at early life stages. Overall, our results suggest that host plants influence mate-searching behaviour of Heliconius. This might also be true for other species of butterflies with more conventional mating strategies, potentially contributing to the diversification of this group of phytophagous insects.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 231-239

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Experimental demonstration of alternative mating tactics of male Ptilothrix fructifera (Hymenoptera, Apidae)


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Reisla Oliveira^{a, ,} and Clemens Schlindwein^{b, 1}

^a Programa de Pós-Graduação em Ciências Biológicas – Zoologia, Universidade Federal da Paraíba, Brazil

^b Laboratório Plebeia – Ecologia de Abelhas e da Polinização, Departamento de Botânica, Universidade Federal de Pernambuco, Brazil

 

Ptilothrix fructifera is a solitary, oligolectic bee dependent on the flowers of Opuntia (Cactaceae). We conducted field studies to identify the mating tactics used by P. fructifera males and to determine whether factors such as male body size and available resource flowers contribute to variation in male mating tactic. Males in a population in southern Brazil showed pronounced variation in body size, but no distinct size classes. Larger males aggressively defended territories of flowering Opuntia plants, the sole pollen source for the females. Smaller males nonaggressively patrolled nonflowering shrubs growing between the nest aggregation and patches of Opuntia. Only unmated females were attractive to males. When offered to males in patrolled shrubs, up to eight males attempted to mate with the same female, but in territories only the territory owner mated with the introduced female. About 10 min after mating, females were unattractive to males. These results identify the species as monogamous and indicate that territoriality is an adaptive mating tactic. Experimental addition of Opuntia flowers to patrolled shrubs showed that nonterritorial males can switch to territorial behaviour. Thus, the number of available flowers together with the number of competitor males determines the ratio of territorial males to patrolling males at a given site. The experiment shows that male P. fructifera show a conditional reproductive strategy in which males adopt alternative tactics according to their size.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 241-247

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Pine weevils modulate defensive behaviour in response to parasites of differing virulence

 

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Darragh E. Ennis^{1, a}, Aoife B. Dillon^{2, a} and Christine T. Griffin ^{, a,}

^a Department of Biology, National University of Ireland Maynooth, Ireland

 

Grooming and avoidance of contaminated areas are among the behavioural defences employed by animals against parasites. Antiparasite defence behaviour is costly in terms of time, energy and/or food foregone and therefore animals are expected to modulate their defences depending on the risk of attack and/or the severity of the symptoms caused. We tested the hypothesis that an insect host invests more in defence against more virulent (more likely to cause death) than less virulent parasites. We tested avoidance and grooming of adult pine weevils, Hylobius abietis, in response to infective juveniles of two species of entomopathogenic nematodes, the more virulent Steinernema carpocapsae and less virulent Heterorhabditis downesi. Weevils avoided feeding on a substrate contaminated with S. carpocapsae but not H. downesi. Weevils also groomed more when their bodies were contaminated with S. carpocapsae than either H. downesi or water. We also made direct observations of nematodes on weevils. When equal numbers of nematodes were applied to weevils more S. carpocapsae than H. downesi moved actively on the weevil’s cuticle. Thus, the differential response of weevils to the two nematode species can be explained by the weevils detecting the more aggressive behaviour of S. carpocapsae than H. downesi, which corresponds to a higher probability of death.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 283-288

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Sex-dependent variation in the floral preferences of the hawkmoth Manduca sexta


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Ruben Alarcón^{a, ,} , Jeffrey A. Riffell^b, Goggy Davidowitz^c, John G. Hildebrand^b and Judith L. Bronstein^d

^a California State University Channel Islands, Camarillo, CA, U.S.A.

^b Division of Neurobiology and Center for Insect Science, Arizona Research Laboratories University of Arizona, Tucson, AZ, U.S.A.

^c Department of Entomology, University of Arizona, Tucson, AZ, U.S.A.

^d Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, U.S.A.

 

Studies of plant–pollinator interactions have often documented species differences in preferences for floral advertisements and rewards. However, the contribution of intraspecific variation in behaviours, especially between sexes, remains less understood. We explored resource preference and resource use by male and female Manduca sexta hawkmoths, relative to two important nectar resources in southern Arizona, U.S.A. Manduca sexta is the major pollinator of one of these species (Datura wrightii, Solanaceae). Because females must also seek out D. wrightii as an oviposition resource, females were predicted to feed upon it more than would males, which should be free to choose the best nectar resource. Using naïve laboratory-reared moths in flight arena experiments, we found that both sexes preferred Datura wrightii over Agave palmeri (Agavaceae). Exposure to only one species and an odourless paper control, however, revealed sex-specific differences in foraging behaviour, with females feeding longer from A. palmeri and males feeding longer from D. wrightii, leading us to reject our hypothesis. Differences in feeding preferences directly translated into differences in energy intake. Females gained significantly more energy than did males by feeding from A. palmeri. We also examined whether behavioural preferences of moths in the laboratory translated into foraging behaviour in the field. Pollen load analysis of moths caught in 2004 showed that females carried significantly more A. palmeri pollen than did males, whereas males carried more D. wrightii pollen than did females. Whereas most studies examine pollination associations at the species level, our results highlight the potential importance of between-sex variation in floral visits.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 289-296

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German cockroach males maximize their inclusive fitness by avoiding mating with kin


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Mathieu Lihoreau^{a, b, ,} and Colette Rivault^{a, 1}

^a UMR 6552, Centre National de la Recherche, Université de Rennes 1, France

^b Research Centre for Psychology, School of Biological and Chemical Sciences, Queen Mary University of London, U.K.

 

Conventional sex roles imply choosy females and nondiscriminating males. However, growing evidence suggests that male choosiness is more common than expected. While male mate choice is clearly linked to high mating investment in sex role-reversed species, factors promoting male mate choice in conventional sex role species are still debated. We addressed this fundamental issue in the German cockroach, Blattella germanica (L.), a group-living species where members of both sexes exercise mutual mate choice to avoid inbreeding. We focused on (1) male potential reproductive rate, (2) male effective reproductive rate, and (3) male reproductive success in relation to female quality. Males tested in situations with unrestrained female availability were able to mate throughout their life, thus revealing a high potential reproductive rate. However, their effective reproductive rate was much more limited under ecologically realistic conditions with restrained female availability. In contradiction with general predictions of sex role theory, mate choice by B. germanica males occurs despite an apparent low mating investment and a male-biased operational sex ratio. The finding that inbred matings were less fertile than outbred matings reveals that kinship is the key factor promoting male choice in this particular case. In the light of inbreeding avoidance theory, we propose that by being choosy cockroach males avoid imposing inbreeding costs on their sisters, thus maximizing their own inclusive fitness via kin selection.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 303-309

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Specialist Bombus vestalis and generalist Bombus bohemicus use different odour cues to find their host Bombus terrestris


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Kirsten Kreuter^a, Robert Twele^{b, 1}, Wittko Francke^{b, 1} and Manfred Ayasse^{a, ,}

^a Institute of Experimental Ecology, Department of Chemical Ecology, University of Ulm, Germany

^b Institute of Organic Chemistry, University of Hamburg, Germany

 

Cuckoo bumblebees (subgenus Psithyrus) are social parasites in colonies of their host bumblebee species (Bombus). In spring, parasitic females awaken from hibernation and start searching for established host nests. Some Psithyrus species are specialized on one host species, whereas generalists parasitize several species. In previous investigations, nest-marking signals of the bumblebee hosts have been shown to play a role in host recognition and discrimination between host and nonhost. We performed behavioural experiments and comparative chemical analyses with the specialist Bombus (Psithyrus) vestalis and the generalist Bombus (Psithyrus) bohemicus to identify semiochemicals that the females use to recognize the common host, Bombus terrestris. In chemical analyses of footprint samples, we mainly identified nonpolar hydrocarbons and polar wax-type esters. Bioassays with nonpolar and polar fractions obtained by solid phase extraction indicate that specialized parasites use a complex bouquet of compounds for host recognition, whereas generalists need only selected substances common to the signals of all of their hosts. The evolutionary significance of the results is discussed.

Animal Behaviour Volume 80, Issue 2, August 2010, Pages 297-302

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Antagonistic effects of floral scent in an insect–plant interaction

 

Carolina E. Reisenman1,*, Jeffrey A. Riffell1, Elizabeth A. Bernays2 and John G. Hildebrand1 carolina@neurobio.arizona.edu

¹Department of Neuroscience, College of Science, University of Arizona, 1040 East Fourth Street, Tucson, AZ 85721-0077, USA

²Department of Entomology, University of Arizona, 1040 East Fourth Street, Tucson, AZ 85721-0077, USA

 

In southwestern USA, the jimsonweed Datura wrightii and the nocturnal moth Manduca sexta form a pollinator–plant and herbivore–plant association. Because the floral scent is probably important in mediating this interaction, we investigated the floral volatiles that might attract M. sexta for feeding and oviposition. We found that flower volatiles increase oviposition and include small amounts of both enantiomers of linalool, a common component of the scent of hawkmoth-pollinated flowers. Because (+)-linalool is processed in a female-specific glomerulus in the primary olfactory centre of M. sexta, we hypothesized that the enantiomers of linalool differentially modulate feeding and oviposition. Using a synthetic mixture that mimics the D. wrightii floral scent, we found that the presence of linalool was not necessary to evoke feeding and that mixtures containing (+)- and/or (−)-linalool were equally effective in mediating this behaviour. By contrast, females oviposited more on plants emitting (+)-linalool (alone or in mixtures) over control plants, while plants emitting (−)-linalool (alone or in mixtures) were less preferred than control plants. Together with our previous investigations, these results show that linalool has differential effects in feeding and oviposition through two neural pathways: one that is sexually isomorphic and non-enantioselective, and another that is female-specific and enantioselective.

Proc. R. Soc. B 7 August 2010 vol. 277 no. 1692 2371-2379

http://rspb.royalsocietypublishing.org/content/277/1692/2371.abstract

Insect Behaviour

Does signalling mitigate the cost of agonistic interactions? A test in a cricket that has lost its song

 

D. M. Logue1,2,*, I. O. Abiola1, D. Rains1, N. W. Bailey3, M. Zuk3 and W. H. Cade1david.logue@upr.edu

¹Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, Canada T1K 3M4

²Departamento de Biología, Universidad de Puerto Rico Mayagüez, PO Box 9000, Mayagüez, PR 00681-9000, USA

³Department of Biology, University of California, Riverside, CA 92521, USA

 

Prevailing models of animal communication assume that signalling during aggressive conflict mitigates the costs of fighting. We tested this assumption by staging dyadic encounters between male field crickets, Teleogryllus oceanicus, under three conditions: (i) both males could sing aggressive songs, (ii) neither male could sing, and (iii) one male could sing but the other could not. We conducted experiments on males from a Hawaiian population from Kauai that has recently evolved signal loss, and males from a Hawaiian population from the Big Island that has not. Among both populations, interactions between two silent males were characterized by higher levels of aggression than interactions involving one or two singing males. Because the level of aggression is strongly related to the cost of fighting, these data demonstrate that signalling mitigates the cost of fighting. In mixed trials, we found no statistically significant differences between the behaviour of calling and non-calling males in either population. We conclude that there is no evidence that the Kauai population exhibits special adaptations to alleviate the costs of signal loss. Finally, we found that males were much more likely to signal after their opponent's retreat than after their own retreat. Aggressive song therefore meets the definition of a ‘victory display’.

Proc. R. Soc. B 22 August 2010 vol. 277 no. 1693 2571-2575

http://rspb.royalsocietypublishing.org/content/277/1693/2571.abstract

 

Insect Biochemistry

Identification of a novel melittin isoform from Africanized Apis mellifera venom

 

References and further reading may be available for this article. To view references and further reading you must purchase this article.Juliana Mozer Sciani^a, Rafael Marques-Porto^a, Airton Lourenço Junior^b, Ricardo de Oliveira Orsi^c, Rui Seabra Ferreira Junior^{b, d}, Benedito Barraviera^{b, d} and Daniel Carvalho Pimenta^{a, d, ,}

^a Laboratório de Bioquímica e Biofísica, Instituto Butantan, Avenida Vital Brasil, 1500, São Paulo, SP 05503-900, Brazil

^b Faculdade de Medicina – UNESP, Distrito de Rubião Junior s/n, Botucatu, SP 18603-970, Brazil

^c Faculdade de Medicina Veterinária e Zootecnia, Distrito de Rubião Junior s/n, Botucatu, SP 18618-000, Brazil

^d Centro de Estudos de Venenos e Animais Peçonhentos – CEVAP - UNESP, Rua José Barbosa de Barros, 1780, Botucatu, SP P.O. Box 577 18610-307, Brazil

 

Apis mellifera, the European honey bee, is perhaps the most studied insect in the Apidae family. Its venom is comprised basically of melittin, phospholipase A₂, histamine, hyaluronidase, cathecolamines and serotonin. Some of these components have been associated to allergic reactions, among several other symptoms. On the other hand, bee mass-stinging is increasingly becoming a serious public health issue; therefore, the development of efficient serum-therapies has become necessary, with a consequent better characterization of the venom. In this work, we report the isolation and biochemical characterization of melittin-S, an isoform of melittin comprising a Ser residue at the 10th position, from the venom of Africanized A. mellifera. This peptide demonstrated to be less hemolytic than melittin and to adopt a less organized secondary structure, as assessed by circular dichroism spectroscopy. Melittin-S venom contents varied seasonally, and the maximum secretion occurred during the (southern) winter months. Data on the variation of the honey bee venom composition are necessary to guide future immunological studies, aiming for the development of an efficient anti-serum against Africanized A. mellifera venom and, consequently, an effective treatment for the victims of mass-stinging.

Peptides Volume 31, Issue 8, August 2010, Pages 1473-1479

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Insect Development

TSC1/2 tumour suppressor complex maintains Drosophila germline stem cells by preventing differentiation

 

Pei Sun¹,², Zhenghui Quan², Bodi Zhang², Tuoqi Wu² and Rongwen Xi²,^* xirongwen@nibs.ac.cn

¹ Graduate program, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100730, China.

² National Institute of Biological Sciences, 7 Science Park Road, Zhongguancun Life Science Park, Beijing 102206, China.

 

Tuberous sclerosis complex human disease gene products TSC1 and TSC2 form a functional complex that negatively regulates target of rapamycin (TOR), an evolutionarily conserved kinase that plays a central role in cell growth and metabolism. Here, we describe a novel role of TSC1/2 in controlling stem cell maintenance. We show that in the Drosophila ovary, disruption of either the Tsc1 or Tsc2 gene in germline stem cells (GSCs) leads to precocious GSC differentiation and loss. The GSC loss can be rescued by treatment with TORC1 inhibitor rapamycin, or by eliminating S6K, a TORC1 downstream effecter, suggesting that precocious differentiation of Tsc1/2 mutant GSC is due to hyperactivation of TORC1. One well-studied mechanism for GSC maintenance is that BMP signals from the niche directly repress the expression of a differentiation-promoting gene bag of marbles (bam) in GSCs. In Tsc1/2 mutant GSCs, BMP signalling activity is downregulated, but bam expression is still repressed. Moreover, Tsc1 bam double mutant GSCs could differentiate into early cystocytes, suggesting that TSC1/2 controls GSC differentiation via both BMP-Bam-dependent and -independent pathways. Taken together, these results suggest that TSC prevents precocious GSC differentiation by inhibiting TORC1 activity and subsequently differentiation-promoting programs. As TSC1/2-TORC1 signalling is highly conserved from Drosophila to mammals, it could have a similar role in controlling stem cell behaviour in mammals, including humans.

Development 137, 2461-2469. August 1, 2010

http://dev.biologists.org/content/137/15/2461.abstract

 

Spps, a Drosophila Sp1/KLF family member, binds to PREs and is required for PRE activity late in development

 

J. Lesley Brown and Judith A. Kassis^*jkassis@mail.nih.gov

Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, 6 Center Drive, Bethesda, MD 20892, USA.

 

The Polycomb group of proteins (PcG) is important for transcriptional repression and silencing in all higher eukaryotes. In Drosophila, PcG proteins are recruited to the DNA by Polycomb-group response elements (PREs), regulatory sequences whose activity depends on the binding of many different sequence-specific DNA-binding proteins. We previously showed that a binding site for the Sp1/KLF family of zinc-finger proteins is required for PRE activity. Here, we report that the Sp1/KLF family member Spps binds specifically to Ubx and engrailed PREs, and that Spps binds to polytene chromosomes in a pattern virtually identical to that of the PcG protein, Psc. A deletion of the Spps gene causes lethality late in development and a loss in pairing-sensitive silencing, an activity associated with PREs. Finally, the Spps mutation enhances the phenotype of pho mutants. We suggest that Spps may work with, or in parallel to, Pho to recruit PcG protein complexes to PREs.

Development 137, 2597-2602. August 1, 2010

http://dev.biologists.org/content/137/15/2597.abstract

 

A two-step Notch-dependant mechanism controls the selection of the polar cell pair in Drosophila oogenesis

 

Caroline Vachias¹, Jean-Louis Couderc¹ and Muriel Grammont¹,^*† muriel.grammont@recherche.univ-lyon1.fr

¹ CNRS 6247, Clermont University, Inserm U931, UMR GReD, UFR Médecine, Clermont-Ferrand F-63001, France.

 

Organisers control the patterning and growth of many tissues and organs. Correctly regulating the size of these organisers is crucial for proper differentiation to occur. Organiser activity in the epithelium of the Drosophila ovarian follicle resides in a pair of cells called polar cells. It is known that these two cells are selected from a cluster of equivalent cells. However, the mechanisms responsible for this selection are still unclear. Here, we present evidence that the selection of the two cells is not random but, by contrast, depends on an atypical two-step Notch-dependant mechanism. We show that this sequential process begins when one cell becomes refractory to Notch activation and is selected as the initial polar cell. This cell then produces a Delta signal that induces a high level of Notch activation in one other cell within the cluster. This Notch activity prevents elimination by apoptosis, allowing its selection as the second polar cell. Therefore, the mechanism used to select precisely two cells from among an equivalence group involves an inductive Delta signal that originates from one cell, itself unable to respond to Notch activation, and results in one other cell being selected to adopt the same fate. Given its properties, this two-step Notch-dependent mechanism represents a novel aspect of Notch action.

Development 137, 2703-2711. August 15, 2010

http://dev.biologists.org/content/137/16/2703.abstract?etoc

 

Drosophila PAT1 is required for Kinesin-1 to transport cargo and to maximize its motility

 

Philippe Loiseau¹,^*, Tim Davies²,^*, Lucy S. Williams¹, Masanori Mishima² and Isabel M. Palacios¹,^† mip22@cam.ac.uk

¹ The Zoology Department, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.

² The Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK

 

Kinesin heavy chain (KHC), the force-generating component of Kinesin-1, is required for the localization of oskar mRNA and the anchoring of the nucleus in the Drosophila oocyte. These events are crucial for the establishment of the anterior-posterior and dorsal-ventral axes. KHC is also essential for the localization of Dynein and for all ooplasmic flows. Interestingly, oocytes without Kinesin light chain show no major defects in these KHC-dependent processes, suggesting that KHC binds its cargoes and is activated by a novel mechanism. Here, we shed new light on the molecular mechanism of Kinesin function in the germline. Using a combination of genetic, biochemical and motor-tracking studies, we show that PAT1, an APP-binding protein, interacts with Kinesin-1, functions in the transport of oskar mRNA and Dynein and is required for the efficient motility of KHC along microtubules. This work suggests that the role of PAT1 in cargo transport in the cell is linked to PAT1 function as a positive regulator of Kinesin motility.

Development 137, 2763-2772. August 15, 2010

http://dev.biologists.org/content/137/16/2763.abstract?etoc

 

Sec5, a member of the exocyst complex, mediates Drosophila embryo cellularization

 

Mala Murthy^*†, Rita O. Teodoro^*, Tamara P. Miller and Thomas L. Schwarz^‡thomas.schwarz@childrens.harvard.edu

The F.M. Kirby Neurobiology Center, Children's Hospital Boston and Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.

 

Cellularization of the Drosophila embryo is the process by which a syncytium of ∼6000 nuclei is subdivided into discrete cells. In order to individualize the cells, massive membrane addition needs to occur by a process that is not fully understood. The exocyst complex is required for some, but not all, forms of exocytosis and plays a role in directing vesicles to appropriate domains of the plasma membrane. Sec5 is a central component of this complex and we here report the isolation of a new allele of sec5 that has a temperature-sensitive phenotype. Using this allele, we investigated whether the exocyst complex is required for cellularization. Embryos from germline clones of the sec5^ts1 allele progress normally through cycle 13. At cellularization, however, cleavage furrows do not invaginate between nuclei and consequently cells do not form. A zygotically translated membrane protein, Neurotactin, is not inserted into the plasma membrane and instead accumulates in cytoplasmic puncta. During cellularization, Sec5 becomes concentrated at the apical end of the lateral membranes, which is likely to be the major site of membrane addition. Subsequently, Sec5 concentrates at the sub-apical complex, indicating a role for Sec5 in the polarized epithelium. Thus, the exocyst is necessary for, and is likely to direct, the polarized addition of new membrane during this form of cytokinesis.

Development 137, 2773-2783. August 15, 2010

http://dev.biologists.org/content/137/16/2773.abstract?etoc

 

 

Insect Ecology

Weaver ants Oecophylla smaragdina encounter nasty neighbors rather than dear enemies

 

Philip S. Newey^1,3, Simon K. A. Robson², and Ross H. Crozier^2,4 philip.newey@unil.ch

¹School of Marine and Tropical Biology, James Cook University, Cairns, Queensland 4878 Australia

²School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811 Australia

 

The evolution of territorial behavior requires that the benefits of territoriality outweigh the costs. The costs are primarily those of territorial defense against encroaching neighbors or against floaters seeking to establish their own territory. One way to reduce the cost of defense might be to restrict serious conflict to encounters with those posing the greatest threat. Studies of many animals have found that less aggression is shown toward neighbors than toward strangers, a phenomenon known as the “dear enemy” effect. However, the opposite can also be true, namely, that more aggression is shown toward neighbors than strangers: the “nasty neighbor” effect. This may be particularly true of group-living species that defend a resource-based territory. Here we show that (1) colonies of the weaver ant Oecophylla smaragdina were able to recognize a greater proportion of workers from neighboring colonies as non-colony members; and (2) when recognized as non-colony members, more aggression was exhibited toward neighbors than non-neighbors. We present for the first time evidence that differential levels of aggression involve both a perceptual and behavioral component. On the other hand, we found no evidence that weaver ant workers were better able to recognize workers from previously unknown colonies or responded more aggressively to them, even after a 10-day period of contact. This contrasts with other species in which rapid learning of the identity of new potential enemies has been demonstrated. We suggest that such a response is unnecessary for weaver ants, as encounters with intruders from non-neighboring colonies are probably rare and of little consequence. This study adds to the growing body of evidence that the nasty neighbor effect may be much more common than the dear enemy effect among group-living species.

Ecology. 2010 91:2366-2372.

http://www.esajournals.org/doi/abs/10.1890/09-0561.1

 

Scaling community structure: how bacteria, fungi, and ant taxocenes differentiate along a tropical forest floor

 

Michael Kaspari^1,2,5, Bradley S. Stevenson³, Jonathan Shik¹, and Jennifer F. Kerekes⁴  mkaspari@ou.edu

¹Graduate Program in EEB, Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019 USA

²Smithsonian Tropical Research Institute, Balboa, Panama

³Graduate Program in EEB, Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019 USA

⁴Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102 USA

 

Taxa with smaller individuals tend to have shorter generation times and higher local abundance and diversity. The scaled specialization hypothesis (SSH) posits that taxocenes of smaller individuals should differentiate more rapidly and thoroughly along physiochemical gradients of a given age and extent. In a Panama rainforest, we evaluated how bacteria, fungi, and ants responded to two such gradients: one topographic and the other arising from nine years of NPK fertilization. Terminal restriction fragment length polymorphism (T-RFLP) delineated bacteria and fungi operational taxonomic units (OTUs); traditional taxonomy delineated the ants. Bacteria had higher local species richness than fungi and ants (averaging 48 vs. 30 vs. 6 OTUs in <0.25 m²). Bacteria OTUs were also more widely distributed (17% of OTUs were found on ≥50% of sample plots compared to 3% for fungi and ants). Consistent with SSH, bacterial composition differed across short-term (+N and +P) and long-term (topographic) gradients; fungal taxocenes differed only along the long-term gradient; and ant taxocenes were homogenous across both. Body size can help predict community responses to a changing environment.

Ecology. 2010 91:2221-2226.

http://www.esajournals.org/doi/abs/10.1890/09-2089.1

 

Nutrient provisioning facilitates homeostasis between tsetse fly (Diptera: Glossinidae) symbionts

 

Anna K. Snyder1, Jason W. Deberry1,†, Laura Runyen-Janecky2 and Rita V. M. Rio1,* rita.rio@mail.wvu.edu

¹Department of Biology, West Virginia University, 53 Campus Drive 5106 LSB, Morgantown, WV 26506, USA

²Department of Biology, University of Richmond, Richmond, VA 23173, USA

 

Host-associated microbial interactions may involve genome complementation, driving-enhanced communal efficiency and stability. The tsetse fly (Diptera: Glossinidae), the obligate vector of African trypanosomes (Trypanosoma brucei subspp.), harbours two enteric Gammaproteobacteria symbionts: Wigglesworthia glossinidia and Sodalis glossinidius. Host coevolution has streamlined the Wigglesworthia genome to complement the exclusively sanguivorous tsetse lifestyle. Comparative genomics reveal that the Sodalis genome contains the majority of Wigglesworthia genes. This significant genomic overlap calls into question why tsetse maintains the coresidence of both symbionts and, furthermore, how symbiont homeostasis is maintained. One of the few distinctions between the Wigglesworthia and Sodalis genomes lies in thiamine biosynthesis. While Wigglesworthia can synthesize thiamine, Sodalis lacks this capability but retains a thiamine ABC transporter (tbpAthiPQ) believed to salvage thiamine. This genetic complementation may represent the early convergence of metabolic pathways that may act to retain Wigglesworthia and evade species antagonism. We show that thiamine monophosphate, the specific thiamine derivative putatively synthesized by Wigglesworthia, impacts Sodalis thiamine transporter expression, proliferation and intracellular localization. A greater understanding of tsetse symbiont interactions may generate alternative control strategies for this significant medical and agricultural pest, while also providing insight into the evolution of microbial associations within hosts.

Proc. R. Soc. B 7 August 2010 vol. 277 no. 1692 2389-2397

http://rspb.royalsocietypublishing.org/content/277/1692/2389.abstract

 

Insect Evolution

Mating tactics determine patterns of condition dependence in a dimorphic horned beetle

 

Robert J. Knell1,* and Leigh W. Simmons2 r.knell@qmul.ac.uk)

¹School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK

²Center for Evolutionary Biology, School of Animal Biology, The University of Western Australia, Crawley, WA 6009, Australia

 

The persistence of genetic variability in performance traits such as strength is surprising given the directional selection that such traits experience, which should cause the fixation of the best genetic variants. One possible explanation is ‘genic capture’ which is usually considered as a candidate mechanism for the maintenance of high genetic variability in sexual signalling traits. This states that if a trait is ‘condition dependent’, with expression being strongly influenced by the bearer's overall viability, then genetic variability can be maintained via mutation-selection balance. Using a species of dimorphic beetle with males that gain matings either by fighting or by ‘sneaking’, we tested the prediction of strong condition dependence for strength, walking speed and testes mass. Strength was strongly condition dependent only in those beetles that fight for access to females. Walking speed, with less of an obvious selective advantage, showed no condition dependence, and testes mass was more condition dependent in sneaks, which engage in higher levels of sperm competition. Within a species, therefore, condition dependent expression varies between morphs, and corresponds to the specific selection pressures experienced by that morph. These results support genic capture as a general explanation for the maintenance of genetic variability in traits under directional selection.

Proc. R. Soc. B 7 August 2010 vol. 277 no. 1692 2347-2353

http://rspb.royalsocietypublishing.org/content/277/1692/2347.abstract

 

Insect Genetics

The genetic structure of populations of an invading pest fruit fly, Bactrocera tryoni, at the species climatic range limit

 

A S Gilchrist¹ and A W Meats¹stuartg@bio.usyd.edu.au

¹Fruit Fly Research Laboratory, School of Biological Sciences A12, University of Sydney, New South Wales, Australia

 

Previous population genetic studies of the Queensland fruit fly, Bactrocera tryoni Froggatt (Diptera: Tephritidae), in its central range have shown barely detectable genetic differentiation across distances of almost 3000 km (F_st=0.003). In this study, we investigated the genetic structuring of southern border populations of B. tryoni, in the region extending from the central population to the recently colonized southern range limit. The expectation was that marginal populations would be small, fragmented population sinks, with local adaptation limited by gene flow or drift. Unexpectedly, we found that the population at the southern extreme of the range was a source population, rather than a sink, for the surrounding region. This was shown by assignment testing of recent outbreaks in an adjoining quarantine area and by indirect migration estimates. Furthermore, populations in the region had formed a latitudinal cline in microsatellite allele frequencies, spanning the region between the central population and the southern range limit. The cline has formed within 250 generations of the initial invasion and appears stable between years. We show that there is restricted gene flow in the region and that effective population sizes are of the order of 10²–10³. Although the cline may result from natural selection, neutral evolutionary processes may also explain our findings.

Heredity (2010) 105, 165–172

http://www.nature.com/hdy/journal/v105/n2/abs/hdy2009163a.html

 

Host-associated divergence and incipient speciation in the yucca moth Prodoxus coloradensis (Lepidoptera: Prodoxidae) on three species of host plants

 

C S Drummond^1,3, H-J Xue^1,2,3, J B Yoder¹ and O Pellmyr¹cdrummon@uidaho.edu

¹Department of Biological Sciences, University of Idaho, Moscow, ID, USA

²Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing, China

 

A wide range of evolutionary processes have been implicated in the diversification of yuccas and yucca moths, which exhibit ecological relationships that extend from obligate plant–pollinator mutualisms to commensalist herbivory. Prodoxus coloradensis (Lepidoptera: Prodoxidae) is a yucca moth, which feeds on the flowering stalks of three Yucca species as larvae, but does not provide pollination service. To test for evidence of host-associated speciation, we examined the genetic structure of P. coloradensis using mitochondrial (cytochrome oxidase I) and nuclear (elongation factor 1 alpha) DNA sequence data. Multilocus coalescent simulations indicate that moths on different host plant species are characterized by recent divergence and low levels of effective migration, with large effective population sizes and considerable retention of shared ancestral polymorphism. Although geographical distance explains a proportion of the mitochondrial and nuclear DNA variation among moths on different species of Yucca, the effect of host specificity on genetic distance remains significant after accounting for spatial isolation. The results of this study indicate that differentiation within P. coloradensis is consistent with the evolution of incipient species affiliated with different host plants, potentially influenced by sex-biased dispersal and female philopatry.

Heredity (2010) 105, 183–196

http://www.nature.com/hdy/journal/v105/n2/abs/hdy2009154a.html

 

Thelytokous parthenogenesis, male clonality and genetic caste determination in the little fire ant: new evidence and insights from the lab

 

J Foucaud^1,3, A Estoup¹, A Loiseau¹, O Rey¹ and J Orivel²julien.foucaud@legs.cnrs-gif.fr

¹INRA, UMR CBGP (INRA/IRD/Cirad/Montpellier SupAgro), Campus international de Baillarguet, Montferrier-sur-Lez, France

²Laboratoire Evolution et Diversité Biologique, UMR-CNRS 5174, Université Toulouse III, 118 route de Narbonne, Toulouse, France

 

Previous studies indicate that some populations of the little fire ant, Wasmannia auropunctata, display an unusual reproduction system polymorphism. Although some populations have a classical haplodiploid reproduction system, in other populations queens are produced by thelytokous parthenogenesis, males are produced by a male clonality system and workers are produced sexually. An atypical genetic caste determination system was also suggested. However, these conclusions were indirectly inferred from genetic studies on field population samples. Here we set up experimental laboratory nests that allow the control of the parental relationships between individuals. The queens heading those nests originated from either putatively clonal or sexual populations. We characterized the male, queen and worker offspring they produced at 12 microsatellite loci. Our results unambiguously confirm the unique reproduction system polymorphism mentioned above and that male clonality is strictly associated with thelytokous parthenogenesis. We also observed direct evidence of the rare production of sexual gynes and arrhenotokous males in clonal populations. Finally, we obtained evidence of a genetic basis for caste determination. The evolutionary significance of the reproduction system polymorphism and genetic caste determination as well as future research opportunities are discussed.

Heredity (2010) 105, 205–212;

http://www.nature.com/hdy/journal/v105/n2/abs/hdy2009169a.html

 

Insect Morphology

Comparative morphology of the head of selected sporophagous and non-sporophagous aleocharinae (Coleoptera: Staphylinidae): Musculature and hypopharynx-prementum complex

 

Daniela Weide ^{1 *}, Margaret K. Thayer ², Alfred F. Newton ², Oliver Betz ¹ b8weda@yahoo.de

¹Institut für Evolution und Ökologie, Evolutionsbiologie der Invertebraten, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28 E, D-72076 Tübingen, Germany
²Field Museum of Natural History, Department of Zoology, Division of Insects, 1400 South Lake Shore Drive, Chicago, Illinois 60605

 

To investigate whether specialization to spore- (or pollen-) feeding in advanced Aleocharinae is mirrored by their head anatomy, we compiled and compared synchrotron X-ray micro-tomography datasets for 11 Aleocharinae in conjunction with previous data for two aleocharine and six outgroup species (two nonstaphylinids, four staphylinids). We describe the presence/absence of head muscles and investigate the variability of points of origin by character mapping analyses. Monophyly of Aleocharinae is supported by the absence of M. 48 (M. tentoriobuccalis anterior), and by changes in the origins of Mm. 1, 2, 17, 18, 28, 29, 30. Within Aleocharinae the origins of the labial muscles (Mm. 28-30) have shifted posteriorly to the gula, which might enhance the movement posterad of the hypopharynx and partly compensate for the loss of M. 48. We also analyzed the general organization of the hypopharynx-prementum complex and the fine structure of the mandibles through SEM studies. In the absence of grinding mandibular molae like those of most mycophagous Coleoptera, seven aleocharine species studied have evolved pseudomolae at the ventral side of the mandibles that replace true molae as secondary grinding surfaces. In these species, the hypopharynx is elevated and displaced anteriorly, bearing a bowl-like depression on its surface that functions as a mortar where spores are ground between the hypopharynx and the mandibles. Two of these species are not yet known to feed on spores or pollen. Another species (Oxypoda alternans) is thought to feed on fungus material but bears no pseudomolae on its mandibles.

J. Morphol. 271:910-931, 2010.

http://www3.interscience.wiley.com/journal/123506625/abstract

 

Cell death shapes embryonic lineages of the central complex in the grasshopper Schistocerca gregaria

 

George Boyan ^*, Zsofia Herbert, Leslie Williams

george.boyan@lmu.de

Developmental Neurobiology Group, Biocenter, Ludwig-Maximilians-Universität München, Grosshadernerstr. 2, 82152 Martinsried, Germany

 

We have investigated cell death in identified lineages of the central complex in the embryonic brain of the grasshopper Schistocerca gregaria. Progeny from these lineages lie in the pars intercerebralis and direct projections to the protocerebral bridge and then the central body via the w, x, y, z tracts. Osmium-ethyl gallate staining reveals pycnotic cells exclusively in cortical regions, and concentrated specifically within the lineages of the W, X, Y, Z neuroblasts. Minimal cell death occurs in a sporadic, nonpatterned manner, in other protocerebral regions. Immunohistochemistry reveals pycnotic cells express the enzyme cleaved Caspase-3 in their cytoplasm and are therefore undergoing programmed cell death (apoptosis). The number of pycnotic bodies in lineages of the pars intercerebralis varies with age: small numbers are present in the Y, Z lineages early in embryogenesis (42%), the number peaks at 67-80%, and then declines and disappears late in embryogenesis. Cell death may encompass up to 20% of a lineage at mid-embryogenesis. Peak cell death occurs shortly after maximum neurogenesis in the Y, Z lineages, and is maintained after neurogenesis has ceased in these lineages. Cell death within a lineage is patterned. Apoptosis is more pronounced among older cells and almost absent among younger cells. This suggests that specific subsets of progeny will be culled from these lineages, and we speculate about the effect of apoptosis on the biochemical profile of such lineages.

J. Morphol. 271:949-959, 2010.  

http://www3.interscience.wiley.com/journal/123350674/abstract

 

 

Insect Neuroscience

Three-dimensional distribution of NO sources in a primary mechanosensory integration center in the locust and its implications for volume signaling

 

Daniel Münch ¹, Swidbert R. Ott ^{2 *}, Hans-Joachim Pflüger ³S.R.Ott@cantab.net

¹Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, 1432 Ås, Norway
²Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK
³Institute of Biology, Neurobiology; Free University Berlin, 14195 Berlin, Germany

 

Nitric oxide (NO) is an evolutionarily conserved mediator of neural plasticity. Because NO is highly diffusible, signals from multiple sources might combine in space and time to affect the same target. Whether such cooperative effects occur will depend on the effective signaling range and on the distances of NO sources to one another and to their targets. These anatomical parameters have been quantified in only few systems. We analyzed the 3D architecture of NO synthase (NOS) expression in a sensory neuropil, the ventral association center (VAC) of the locust. High-resolution confocal microscopy revealed NOS immunoreactive fiber boutons in submicrometer proximity to both the axon terminals of sensory neurons and their postsynaptic target, interneuron A4I1. Pharmacological manipulation of NO signaling affected the response of A4I1 to individual wind-puff stimuli and the response decrement during repetitive stimulation. Mapping NOS immunoreactivity in defined volumes around dendrites of A4I1 revealed NOS-positive fiber boutons within 5 m of nearly every surface point. The mean distances between neighboring NOS-boutons and between any point within the VAC and its nearest NOS-bouton were likewise about 5 m. For an NO signal to convey the identity of its source, the effective signaling range would therefore have to be less than 5 m, and shorter still when multiple boutons release NO simultaneously. The architecture is therefore well suited to support the cooperative generation of volume signals by interaction between the signals from multiple active boutons.

J. Comp. Neurol. 518:2903-2916, 2010.

http://www3.interscience.wiley.com/journal/123350184/abstract

 

Histamine-immunoreactive local neurons in the antennal lobes of the hymenoptera

 

Andrew M. Dacks ^{1 *}, Carolina E. Reisenman ¹, Angelique C. Paulk ², Alan J. Nighorn ¹adacks@email.arizona.edu

¹Department of Neuroscience, The University of Arizona, Tucson, Arizona 85721
²Queensland Brain Institute, The University of Queensland, Brisbane, Queensland 4000, Australia

 

Neural networks receive input that is transformed before being sent as output to higher centers of processing. These transformations are often mediated by local interneurons (LNs) that influence output based on activity across the network. In primary olfactory centers, the LNs that mediate these lateral interactions are extremely diverse. For instance, the antennal lobes (ALs) of bumblebees possess both -aminobutyric acid (GABA)- and histamine-immunoreactive (HA-ir) LNs, and both are neurotransmitters associated with fast forms of inhibition. Although the GABAergic network of the AL has been extensively studied, we sought to examine the anatomical features of the HA-ir LNs in relation to the other cellular elements of the bumblebee AL. As a population, HA-ir LNs densely innervate the glomerular core and sparsely arborize in the outer glomerular rind, overlapping with the terminals of olfactory receptor neurons. Individual fills of HA-ir LNs revealed heavy arborization of the outer ring of a single principal glomerulus and sparse arborization in the core of other glomeruli. In contrast, projection neurons and GABA-immunoreactive LNs project throughout the glomerular volume. To provide insight into the selective pressures that resulted in the evolution of HA-ir LNs, we determined the phylogenetic distribution of HA-ir LNs in the AL. HA-ir LNs were present in all but the most basal hymenopteran examined, although there were significant morphological differences between major groups within the Hymenoptera. The ALs of other insect taxa examined lacked HA-ir LNs, suggesting that this population of LNs arose within the Hymenoptera and underwent extensive morphological modification.

J. Comp. Neurol. 518:2917-2933, 2010.

http://www3.interscience.wiley.com/journal/123328337/abstract

 

Development-based compartmentalization of the Drosophila central brain

Wayne Pereanu ^{1 2 *}, Abilasha Kumar ³, Arnim Jennett ², Heinrich Reichert ³, Volker Hartenstein ¹neromike@gmail.com

¹Department of Molecular Cell and Developmental Biology, University of California Los Angeles, Los Angeles, California 90095
²HHMI Janelia Farm Research Campus, Ashburn, Virginia 20147
³Biozentrum, University of Basel, CH-4056 Basel, Switzerland

The neuropile of the Drosophila brain is subdivided into anatomically discrete compartments. Compartments are rich in terminal neurite branching and synapses; they are the neuropile domains in which signal processing takes place. Compartment boundaries are defined by more or less dense layers of glial cells as well as long neurite fascicles. These fascicles are formed during the larval period, when the approximately 100 neuronal lineages that constitute the Drosophila central brain differentiate. Each lineage forms an axon tract with a characteristic trajectory in the neuropile; groups of spatially related tracts congregate into the brain fascicles that can be followed from the larva throughout metamorphosis into the adult stage. Here we provide a map of the adult brain compartments and the relevant fascicles defining compartmental boundaries. We have identified the neuronal lineages contributing to each fascicle, which allowed us to compare compartments of the larval and adult brain directly. Most adult compartments can be recognized already in the early larval brain, where they form a protomap of the later adult compartments. Our analysis highlights the morphogenetic changes shaping the Drosophila brain; the data will be important for studies that link early-acting genetic mechanisms to the adult neuronal structures and circuits controlled by these mechanisms. J. Comp. Neurol. 518:2996-3023, 2010

http://www3.interscience.wiley.com/journal/123328355/abstract

 

Frequency processing at consecutive levels in the auditory system of bush crickets (tettigoniidae)

 

Tim Daniel Ostrowski ^*, Andreas Stumpnerostrowskit@missouri.edu

Georg-August-University Göttingen, Johann-Friedrich-Blumenbach Institute for Zoology and Anthropology, Cellular Neurobiology, 37073 Göttingen, Germany

 

We asked how processing of male signals in the auditory pathway of the bush cricket Ancistrura nigrovittata (Phaneropterinae, Tettigoniidae) changes from the ear to the brain. From 37 sensory neurons in the crista acustica single elements (cells 8 or 9) have frequency tuning corresponding closely to the behavioral tuning of the females. Nevertheless, one-quarter of sensory neurons (approximately cells 9 to 18) excite the ascending neuron 1 (AN1), which is best tuned to the male's song carrier frequency. AN1 receives frequency-dependent inhibition, reducing sensitivity especially in the ultrasound. When recorded in the brain, AN1 shows slightly lower overall activity than when recorded in the prothoracic ganglion close to the spike-generating zone. This difference is significant in the ultrasonic range. The first identified local brain neuron in a bush cricket (LBN1) is described. Its dendrites overlap with some of AN1-terminations in the brain. Its frequency tuning and intensity dependence strongly suggest a direct postsynaptic connection to AN1. Spiking in LBN1 is only elicited after summation of excitatory postsynaptic potentials evoked by individual AN1-action potentials. This serves a filtering mechanism that reduces the sensitivity of LBN1 and also its responsiveness to ultrasound as compared to AN1. Consequently, spike latencies of LBN1 are long (>30 ms) despite its being a second-order interneuron. Additionally, LBN1 receives frequency-specific inhibition, most likely further reducing its responses to ultrasound. This demonstrates that frequency-specific inhibition is redundant in two directly connected interneurons on subsequent levels in the auditory system.

J. Comp. Neurol. 518:3101-3116, 2010.

http://www3.interscience.wiley.com/journal/123328347/abstract

 

Multiple neuropeptides in the Drosophila antennal lobe suggest complex modulatory circuits

 

Mikael A. Carlsson ^{1 *}, Max Diesner ², Joachim Schachtner ², Dick R. Nässel ^{1 *}

¹Department of Zoology, Stockholm University, S-10691, Stockholm, Sweden
²Department of Biology, Animal Physiology, Philipps University, 35032, Marburg, Germanymikael.carlsson@zoologi.su.se dnassel@zoologi.su.se

 

The fruitfly, Drosophila, is dependent on its olfactory sense in food search and reproduction. Processing of odorant information takes place in the antennal lobes, the primary olfactory center in the insect brain. Besides classical neurotransmitters, earlier studies have indicated the presence of a few neuropeptides in the olfactory system. In the present study we made an extensive analysis of the expression of neuropeptides in the Drosophila antennal lobes by direct profiling using matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry and immunocytochemistry. Neuropeptides from seven different precursor genes were unambiguously identified and their localization in neurons was subsequently revealed by immunocytochemistry. These were short neuropeptide F, tachykinin related peptide, allatostatin A, myoinhibitory peptide, SIFamide, IPNamide, and myosuppressin. The neuropeptides were expressed in subsets of olfactory sensory cells and different populations of local interneurons and extrinsic (centrifugal) neurons. In some neuron types neuropeptides were colocalized with classical neurotransmitters. Our findings suggest a huge complexity in peptidergic signaling in different circuits of the antennal lobe.

J. Comp. Neurol. 518:3359-3380, 2010.

http://www3.interscience.wiley.com/journal/123453356/abstract

 

Sparse but specific temporal coding by spikes in an insect sensory-motor ocellar pathway

 

Peter J. Simmons^1,* and Rob R. de Ruyter van Steveninck² p.j.simmons@ncl.ac.uk

¹ Institute of Neuroscience and School of Biology, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
² Department of Physics, Indiana University, Bloomington IN 47405, USA

 

We investigate coding in a locust brain neuron, DNI, which transforms graded synaptic input from ocellar L-neurons into axonal spikes that travel to excite particular thoracic flight neurons. Ocellar neurons are naturally stimulated by fluctuations in light collected from a wide field of view, for example when the visual horizon moves up and down. We used two types of stimuli: fluctuating light from a light-emitting diode (LED), and a visual horizon displayed on an electrostatic monitor. In response to randomly fluctuating light stimuli delivered from the LED, individual spikes in DNI occur sparsely but are timed to sub-millisecond precision, carrying substantial information: 4.5–7 bits per spike in our experiments. In response to these light stimuli, the graded potential signal in DNI carries considerably less information than in presynaptic L-neurons. DNI is excited in phase with either sinusoidal light from an LED or a visual horizon oscillating up and down at 20 Hz, and changes in mean light level or mean horizon level alter the timing of excitation for each cycle. DNI is a multimodal interneuron, but its ability to time spikes precisely in response to ocellar stimulation is not degraded by additional excitation. We suggest that DNI is part of an optical proprioceptor system, responding to the optical signal induced in the ocelli by nodding movements of the locust head during each wing-beat.

Journal of Experimental Biology 213, 2629-2639 (2010)
http://jeb.biologists.org/cgi/content/abstract/213/15/2629

 

Evidence for the possible existence of a second polarization-vision pathway in the locust brain

 

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Basil el Jundi^a and Uwe Homberg ^{, a,}

^a Fachbereich Biologie, Tierphysiologie, Philipps-Universität Marburg, D-35032 Marburg, Germany

 

For spatial orientation and navigation, many insects derive compass information from the polarization pattern of the blue sky. The desert locust Schistocerca gregaria detects polarized light with a specialized dorsal rim area of its compound eye. In the locust brain, polarized-light signals are passed through the anterior optic tract and tubercle to the central complex which most likely serves as an internal sky compass. Here, we suggest that neurons of a second visual pathway, via the accessory medulla and posterior optic tubercle, also provide polarization information to the central complex. Intracellular recordings show that two types of neuron in this posterior pathway are sensitive to polarized light. One cell type connects the dorsal rim area of the medulla with the medulla and accessory medulla, and a second type connects the bilaterally paired posterior optic tubercles. Given the evidence for a role of the accessory medulla as the master clock controlling circadian changes in behavioral activity in flies and cockroaches, our data open the possibility that time-compensated polarized-light signals may reach the central complex via this pathway for time-compensated sky-compass navigation.

Journal of Insect Physiology Volume 56, Issue 8, August 2010, Pages 971-979

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T3F-505GHH7-1&_user=10&_coverDate=08%2F31%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=38bb04297e44fc02777fd423b01fb411

 

Visualizing retinotopic half-wave rectified input to the motion detection circuitry of Drosophila

 

Dierk F Reiff,Johannes Plett,Marco Mank,Oliver Griesbeck& Alexander Borst reiff@neuro.mpg.de

Max Planck Institute of Neurobiology, Martinsried, Germany.Journal name:

DOI:

 

In the visual system of Drosophila, photoreceptors R1–R6 relay achromatic brightness information to five parallel pathways. Two of them, the lamina monopolar cells L1 and L2, represent the major input lines to the motion detection circuitry. We devised a new method for optical recording of visually evoked changes in intracellular Ca²⁺ in neurons using targeted expression of a genetically encoded Ca²⁺ indicator. Ca²⁺ in single terminals of L2 neurons in the medulla carried no information about the direction of motion. However, we found that brightness decrements (light-OFF) induced a strong increase in intracellular Ca²⁺ but brightness increments (light-ON) induced only small changes, suggesting that half-wave rectification of the input signal occurs. Thus, L2 predominantly transmits brightness decrements to downstream circuits that then compute the direction of image motion.

Nature NeuroscienceVolume:13,Pages:973–978Year published: (2010)

http://www.nature.com/neuro/journal/v13/n8/abs/nn.2595.html?lang=en

 

Insect Olfaction

Spatial representation of alarm pheromone information in a secondary olfactory centre in the ant brain

 

Nobuhiro Yamagata and Makoto Mizunami*mizunami@sci.hokudai.ac.jp

Graduate School of Life Sciences, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan

 

Pheromones play major roles in intraspecific communication in many animals. Elaborated communication systems in eusocial insects provide excellent materials to study neural mechanisms for social pheromone processing. We previously reported that alarm pheromone information is processed in a specific cluster of glomeruli in the antennal lobe of the ant Camponotus obscuripes. However, representation of alarm pheromone information in a secondary olfactory centre is unknown in any animal. Olfactory information in the antennal lobe is transmitted to secondary olfactory centres, including the lateral horn, by projection neurons (PNs). In this study, we compared distributions of terminal boutons of alarm pheromone-sensitive and -insensitive PNs in the lateral horn of ants. Distributions of their dendrites largely overlapped, but there was a region where boutons of pheromone-sensitive PNs, but not those of pheromone-insensitive PNs, were significantly denser than in the rest of the lateral horn. Moreover, most of a major type of pheromone-sensitive efferent neurons from the lateral horn extended dendritic branches in this region, suggesting specialization of this region for alarm pheromone processing. This study is the first study to demonstrate the presence of specialized areas for the processing of a non-sexual, social pheromone in the secondary olfactory centre in any animal.

Proc. R. Soc. B 22 August 2010 vol. 277 no. 1693 2465-2474

http://rspb.royalsocietypublishing.org/content/277/1693/2465.abstract

 

 

Edited by Xin-Cheng Zhao

2010-08-05

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